Explain the aldol condensation reaction.

(N/A) Aldol condensation:
$(i)$ Aldehydes and ketones possessing at least one $\alpha$-hydrogen atom undergo a reaction in the presence of a dilute alkali (base) to form $\beta$-hydroxy aldehydes (aldol) or $\beta$-hydroxy ketones (ketol),respectively. This reaction is known as aldol condensation.
$(ii)$ The name 'aldol' is derived from the two functional groups present in the product: aldehyde and alcohol.
$(iii)$ Upon heating,these aldol and ketol products readily lose a water molecule to form $\alpha, \beta$-unsaturated carbonyl compounds. This overall process is also referred to as aldol condensation.
$(b)$ Example: Aldol condensation of acetaldehyde $(CH_3CHO)$:
$2CH_3CHO$ $\xrightarrow{\text{dil. NaOH}} CH_3CH(OH)CH_2CHO$ $\xrightarrow{\Delta, -H_2O} CH_3CH=CHCHO$ (But$-2-$enal).
$(c)$ Key points:
$(i)$ Only aldehydes and ketones with at least one $\alpha$-hydrogen atom undergo this reaction because $\alpha$-hydrogens are acidic in nature.
$(ii)$ Compounds like benzaldehyde $(C_6H_5CHO)$ and trimethylacetaldehyde $((CH_3)_3CCHO)$ do not possess $\alpha$-hydrogen atoms and therefore do not undergo aldol condensation.